1. Field of the Invention
This invention relates to a system for decomposing a gaseous or liquid organic compound.
2. Description of the Prior Art
Organic compounds such as trichloroethylene and tetrachloroethylene have been used over a long term of years as detergents and solvents in the field related to semiconductors as well as the field of metal oil cleaning, dry cleaning and the like because of their high solvency.
However, it has been recently ascertained that carcinogen is contained in these chlorine organic compounds, so that their harmfulness constitutes a social problem, resulting in enforcement of regulation on emission of the chlorine organic compounds. For this reason, in places of industries that have emitted a large quantity of chlorine organic compounds after use in the past, pollution of the soil, as well as pollution of the ground water, within the sites and the peripheries thereof is at serious issue.
In addition, polluted gas containing a certain kind of organic compound emits an offensive odor, which sometimes causes environmental deterioration.
To purify the ground water, there has been normally the need for regeneration of an organic compound by pumping up polluted ground water with a storage pump and then removing the organic compound contained in the pumped-up ground water by adsorption with activated carbon, or alternatively, separating the organic compound contained in the polluted ground water by adsorption with the activated carbon or the like after separating the organic compound as exhaust gas with the aeration equipment. For this reason, the large-scaled adsorption equipment using the activated carbon is required for places that are polluted in high concentration over a wide area, so that a burden on the facility cost, as well as the running cost, constitutes a problem.
In addition, to purify the soil, there has been the need for regeneration of an organic compound by drawing soil gas by suction and then removing the organic compound contained in the soil gas by adsorption with activated carbon. For this reason, the large-scaled adsorption equipment using the activated carbon is also required for places that are polluted in high concentration over a wide area, so that a burden on the facility cost, as well as the running cost, constitutes a problem.
If making an attempt to remove the organic compound contained in the soil gas by adsorption solely with the activated carbon, the activated carbon needs to be exchanged frequently, and besides, a tremendous labor, as well as an enormous expense, is required for exchange and regeneration of the activated carbon, disposal of the wasted activated carbon and the like, resulting in a remarkable increase in burden on enterprises to realize purification of the soil.
On the other hand, a technique for decomposing an organic compound by ultraviolet irradiation is well known. For surface cleaning of a semiconductor wafer, for instance, an Excimer lamp and the like are used for irradiation of high energy ultraviolet rays (whose wavelength is 172 nm) to decompose the organic compound on the wafer surface. Irradiation of high-energy ultraviolet rays as described above results in decomposition of the organic compound in an extremely short period of time. However, the Excimer lamp is exceptionally expensive and needs not only the enormous facility cost but also the extremely high power consumption, so that it is supposed that the Excimer lamp is not suited to be of practical use for purification of the soil.
In addition, if making an attempt to decompose the organic compound by ultraviolet irradiation with a low pressure mercury lamp, a middle pressure mercury lamp and high pressure mercury lamp that are available at low cost, an unstably reactive substance such as hydrogen chloride and halacetic acid is produced as an intermediate product, and as a result, it takes much time to decompose the intermediate product into up to stable substances.
In this connection, in Japanese Patent Application Laid-open No. 8-24335, there is disclosed a method for decomposing an organic chlorine compound by steps of decomposing the organic chlorine compound into up to a reaction intermediate having chlorine atoms by irradiating ultraviolet rays inclusive of ultraviolet rays whose wavelength is not more than 300 nm to gas containing the organic chlorine compound, and further decomposing the reaction intermediate through the biological treatment.
The biological treatment has the advantage of adaptability to the environment, whereas it presents problems such as a difficulty in managing the treatment and a need for much time to conduct the treatment due to the extremely slow proceeding of decomposition. In particular, it is supposed that the biological treatment is not enough to cope with high concentration pollution.